Today, millions of medical devices are used worldwide to treat or support patients. Patients expect that each device has been rigorously tested for functionality, performance, sterility and safety prior to being sold. The biological safety (biocompatibility) of a device is established for both short-term (acute) and longtime (chronic) safety risks to patients and device users. Medical device manufacturers must investigate their devices thoroughly to meet these expectations and receive approval to market their devices. While manufacturers most often use the internationally accepted ISO 10993 standard series “Biological evaluation of medical devices,” many countries have additional requirements or interpret this standard differently. Based upon the categorization of the device under evaluation, the manufacturer should develop an appropriate testing strategy. The test strategy should also take into account where the device will be submitted for registration and marketed, e.g., EU, USA, Japan, China, etc., because countries often have specific requirements for the biological evaluation. This article focuses on approval aspects in the European Union (CE Mark) and United States (FDA Approval).